1. Technical Field of the Invention
The present invention relates to a method of manufacturing coil for stators mounted in rotary electric machines, and in particular, to a method of manufacturing coil (also referred to as a stator coil) used for stators mounted in rotary electric machines which are loaded on vehicles.
2. Related Art
In recent years, small size, high power and high quality have been demanded of rotary electric machines used as electric motors and electric generators. Taking rotary electric machines loaded on vehicles as an example, the space for loading such a rotary electric machine has been increasingly reduced, while the output has been increasingly required to be enhanced.
Conventional rotary electric machines that have been known include a type of rotary electric machine, as described in Japanese Patent No. 3894004, for example, having a stator wound with a stator coil which is formed of continuous windings. Such a rotary electric machine is provided with a stator whose stator coil has three-phase windings formed of twelve element wires, providing a structure where twenty-four end portions of the element wires are axially projected from an axial end face of the stator core. Therefore, the stator needs a large space on an outer side of the axial end face of the stator core, for connecting the end portions of the element wires with each other, making large the axial dimension of the stator.
To take a measure for this, the applicant of the present application previously filed an application (e.g., Japanese Patent Application No. 2007-305104) concerning a stator for rotary electric machines, which stator is able to suppress the increase in the size of the stator. This stator has a stator coil in which a plurality of phase windings are accommodated in a plurality of slots of the stator core, while being wound about the stator core to form an undulation in the circumferential direction. Each phase wire is constituted of a first winding portion formed of a continuous wire and a second winding portion formed of a continuous wire and serially connected to the first winding portion. The joint portion between the first and second winding portions is disposed in a slot of the stator core. Accordingly, this stator coil can reduce the number of end portions of the phase windings projected from the axial end face of the stator core. Thus, the space needed for mutually connecting the end portions of the phase windings can be reduced, whereby the increase in the size of the stator can be suppressed.
For example, methods of manufacturing a stator coil formed of continuous windings include a method as presented below. First, a plurality of shaped wire members are shaped from electrically conductive wires. In each of the shaped wire members, a plurality of juxtaposed straight portions are connected through a plurality of turn portions. The shaped wire members are integrated with each other to form an integrated body. In the integrated body, a plurality of pairs of shaped wire members, each pair consisting of one shaped wire member and another shaped wire member, are juxtaposed in the longitudinal direction of the integrated body. Each pair of shaped wire members constituting the integrated body has a plurality of straight superposed portions in the longitudinal direction of the integrated body. The straight superposed portions are formed by superposing a plurality of straight portions of one shaped wire member with a plurality of respective straight portions of another shaped wire member.
Thus, in the integrated body, a plurality of straight superposed portions are juxtaposed in the longitudinal direction of the integrated body. The integrated body is wound up about a core member with a predetermined number of winding turns to form a wound-up body. The wound-up body has a plurality of straight stack portions in the circumferential direction, in each of which a plurality of straight superposed portions in one pair of shaped wire members are radially stacked.
In the wound-up body obtained in this way, the straight stack portions of are disposed in the respective slots of the stator core, with the turn portions being disposed outside the slots, to thereby provide a stator coil. However, the above manufacturing method is likely to cause offset in the superposition of the straight portions of the straight superposed portions, or to provide uneven intervals between adjacent straight superposed portions in the integrated body.
Therefore, in an obtained wound-up body, it is likely that offset is caused in the superposition of the plurality of straight portions in the respective straight stack portions, or the intervals are uneven between adjacent straight stack portions. Therefore, this may degrade the accuracy in the alignment of the straight portions in the respective slots, or may degrade the uniformity in the intervals (pitch) between the straight stack portions disposed in adjacent slots, when the straight stack portions of the stator coil are disposed in the respective slots of the stator core. Degradation in the alignment accuracy of the straight portions or degradation in the uniformity of pitch may lead to low slot occupancy in the stator, or power reduction of the rotary electric machine using the stator.